Four New Actinide Chalcogenides Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5: Crystal Structures and Physical Properties

Four new actinide chalcogenidesnamely, Ba2Cu4USe6, Ba2Cu2ThSe5, Ba2Cu2USe5, and Sr2Cu2US5were synthesized via solid-state methods at 1173 K. Single-crystal X-ray diffraction studies show that Ba2Cu4USe6 crystallizes in a new structure type in space group C2h5–P21/c of the monoclinic system, whereas the three other compounds are isostructural and adopt the Ba2Cu2US5 structure type in space group C2h3–C2/m, also of the monoclinic system. These Ak/Cu/An/Q structures (Ak = alkaline-earth metal; An = actinide; Q = chalcogen) have no short Q–Q interactions and, hence, are charge-balanced with Ak2+, Cu1+, An4+, and Q2–. Crystal structures of all these compounds are two-dimensional and feature layers that are separated by Ba2+ cations. The compositions of these layers differ. In the structure of Ba2Cu4USe6, the ∞2[Cu4USe64–] layers comprising USe6 octahedra and CuSe4 tetrahedra stack perpendicular to the a-axis. These ∞2[Cu4USe64–] layers show short Cu–Cu interactions. In the three isostructural Ak2Cu2AnQ5 compounds, AnQ6 octahedra and CuQ4 tetrahedra are connected along the c-axis in the sequence “...oct tet tet oct tet tet...” to form the ∞2[Cu2AnQ54–] layers. Resistivity, optical, and DFT calculations show semiconducting behavior for these compounds.